This invention relates to closing thermoplastic tubes having an open end so as to form a tube bottom from the material of the previously open ended tube.
It is known that the end of an open tube comprising a thermoplastic material may be closed without attaching a separate piece to form the bottom. U.S. Pat. No. 2,876,496--Murphy, Jr. discloses a method and apparatus for closing an open ended tube at one end by initially heating the end so as to flare the end outwardly. A sleeve is then advanced over the flared end to collapse the outwardly flared end. Subsequently, a mandrel is inserted into the tube and a die or mold cooperates with the tube and the sleeve to close the collapsed end. There is no heating of the mandrel which is inserted into the tube prior to closing. It is significant that the patent only discloses the closing of small size tubes, e.g., catheter tubing having an internal diameter of 0.190 inches.
U.S. Pat. No. 3,300,559--Baehr also discloses a method and apparatus for closing the open end of thermoplastic tubes. The open end of the tube which is mounted on a mandrel is brought into contact with a cup-like member. A heating element is then brought into heating engagement with the cup-like member on the side opposite the open end while the mandrel carrying the tube is advanced so as to collapse and close the end of the tube. The heating member is then retracted while the tube remains in contact with the cup-like member. The cup-like member is then cooled and the closed tube is subsequently retracted from the cooled cup-like member. There is no heating of the mandrel.
U.S. Pat. No. 3,509,252--Baehr discloses a method and apparatus similar to that disclosed in the aforesaid Baehr patent except that the cup-like member is heated directly. The cup-like member does not necessarily completely close the end of the tube. Rather complete closing of the end of the tube to achieve the finished bottom shape is provided by another cup-like member which is relatively cool. Neither Baehr patent discloses the heating of the mandrel heated in advance of contact by a cup-like member.